Printed circuit boards usually include integral plated-through holes to receive the leads of electronic components mounted on the board. The lead socket was developed to allow a component to be plugged into the board and yet be removed at some later time for replacement or repair. The socket and hole are predesigned for a mutual fit whereby the socket, after being pressed into the hole, acts as an intermediate electrical conductor between the lead and hole plating. The socket bottom usually terminates in deformable fingers of uniform length which bend inward to meet the inserted lead. The socket at its outer circumference frictionally engages the plated bore of the hole; the lead, when inserted, similarly engages the finger tips of the socket. As there is no permanent bonding of the lead to the plating, as in a solder joint, the lead is removable. Pertinent examples of known lead sockets in the art may be found in U.S. Pat. Nos. 4,097,101, 4,175,810, and 4,186,990.
Because each finger is fixed at one end only, and must deform as it is engaged by the advancing edge of the lead tip, the finger can be modeled as a cantilever beam. The deflection y of the beam thus varies according to the cube of its length as defined by the equation: EQU y=Pl.sup.3 /3EI
where P=load, l=length, E=modulus of elasticity, and I=moment of inertia. Therefore, when all other variables are held constant, the length of a socket finger determines its relative compliance. Further, the length of the longest finger substantially establishes the height, or profile, of the socket.
It is advantageous to reduce the profile of the socket to reduce component height on densely-packed board arrays. However, a low-profile lead socket of conventional design would have a shorter, and thus less compliant, socket finger. Less-than-adequate compliance requires, among other things, a higher lead insertion force and stiffer leads which, in turn, would reduce the useable lifetime of a low-profile socket and would precipitate greater damage to the lead.